levels at their present values would be an attractive prospect. The second is that there are serious reasons to fear that air travelers will be less safe in the years ahead than in the ones just ended. But the third premise, embodied in the question mark, is that one can realistically hope that aviation safety will not diminish despite looming hazards In the pages ahead, we will offer arguments for all of these premises. We will rely on empirical evidence, but also somewhat on interpretation. The reader, therefore, might therefore find some of the arguments more convincing than others. Thus, s/he might reach a different synthesis of the evidence than does the author We start the analysis in the next section, with a discussion about how one might measure(passenger) aviation safety. Then we proceed to some overall calculations about recent safety levels. We thereafter identify three potential dangers that caused very few First-World deaths in the 1990s but which could cause many fatalities in coming years. Then, without disavowing this assessment, we introduce some points in that work against pessimism. In the final section, we reach a prognosis of sorts Measuring Passenger Air Safety We focus on passenger safety, and posit that the traveler's greatest fear in aviation is of being killed in a crash. Under this assumption, information about the likelihood of that outcome takes on overarching importance. But there is a difficulty: several of the most common"barometers "about aviation safety bear an unknown relationship to mortality risk per flight. Here we illustrate the point by considering two such barometers. others are discussed in barnett and Wang Fatal Accidents per 100.000 Flying Hours This metric is among those used by the US National Transportation Safety board to measure airline safety performance. Thus, the agency reported in 1997 that scheduled US carriers averaged 0. 2 fatal accidents per 100,000 flying hours over 1993-96, half the corresponding rate for the four-year period a decade earlier The statistic, alas, has two shortcomings: its numerator and its denominator. The generic term"fatal accidents "includes all accidents that cause at least one death, and thus blurs the distinction between a crash that kills one passenger out of 250 and another that retardant materials) that reduce fatalities but do not prevent them ovements(e.g.fire- kills 250 out of 250. The measure gives no weight to safety impI Moreover, safety statistics based on total"flying hours"(or, for that matter, miles covered)are questionable because the heavy majority of accidents occur during the takeoff/climb and descent/landing phases of flight. If average trip time changes from period to and ident rates based on flight duration could change for reasons having nothing to do with safety2 levels at their present values would be an attractive prospect. The second is that there are serious reasons to fear that air travelers will be less safe in the years ahead than in the ones just ended. But the third premise, embodied in the question mark, is that one can realistically hope that aviation safety will not diminish despite looming hazards. In the pages ahead, we will offer arguments for all of these premises. We will rely on empirical evidence, but also somewhat on interpretation. The reader, therefore, might therefore find some of the arguments more convincing than others. Thus, s/he might reach a different synthesis of the evidence than does the author. We start the analysis in the next section, with a discussion about how one might measure (passenger) aviation safety. Then we proceed to some overall calculations about recent safety levels. We thereafter identify three potential dangers that caused very few First-World deaths in the 1990’s but which could cause many fatalities in coming years. Then, without disavowing this assessment, we introduce some points in that work against pessimism. In the final section, we reach a prognosis of sorts. Measuring Passenger Air Safety We focus on passenger safety, and posit that the traveler’s greatest fear in aviation is of being killed in a crash. Under this assumption, information about the likelihood of that outcome takes on overarching importance. But there is a difficulty: several of the most common “barometers” about aviation safety bear an unknown relationship to mortality risk per flight. Here we illustrate the point by considering two such barometers; others are discussed in Barnett and Wang1 . Fatal Accidents per 100,000 Flying Hours This metric is among those used by the US National Transportation Safety Board to measure airline safety performance. Thus, the agency reported in 1997 that scheduled US carriers averaged 0.2 fatal accidents per 100,000 flying hours over 1993-96, half the corresponding rate for the four-year period a decade earlier. The statistic, alas, has two shortcomings: its numerator and its denominator. The generic term “fatal accidents” includes all accidents that cause at least one death, and thus blurs the distinction between a crash that kills one passenger out of 250 and another that kills 250 out of 250. The measure gives no weight to safety improvements (e.g. fire￾retardant materials) that reduce fatalities but do not prevent them. Moreover, safety statistics based on total “flying hours” (or, for that matter, miles covered) are questionable because the heavy majority of accidents occur during the takeoff/climb and descent/landing phases of flight. If average trip time changes from one period to another, accident rates based on flight duration could change for reasons having nothing to do with safety